expression: implement vectorized evaluation for builtinCastStringAsRealSig

[pingyu]

PCP #12105

What problem does this PR solve?

Implement vectorized evaluation for builtinCastStringAsRealSig at #12105

What is changed and how it works?

It gets faster about 20%.

Check List

Tests

• Unit test

 > GO111MODULE=on go test -check.f TestVectorizedBuiltinCastFunc
PASS: builtin_cast_vec_test.go:132: testEvaluatorSuite.TestVectorizedBuiltinCastFunc	0.135s
OK: 1 passed
PASS
ok  	github.com/pingcap/tidb/expression	0.162s

• Benchmark

> go test -v -benchmem -bench=BenchmarkVectorizedBuiltinCastFunc -run=BenchmarkVectorizedBuiltinCastFunc -args builtinCastStringAsRealSig
goos: darwin
goarch: amd64
pkg: github.com/pingcap/tidb/expression
BenchmarkVectorizedBuiltinCastFunc/builtinCastStringAsRealSig-VecBuiltinFunc-12         	   12048	     96351 ns/op	       0 B/op	       0 allocs/op
BenchmarkVectorizedBuiltinCastFunc/builtinCastStringAsRealSig-NonVecBuiltinFunc-12      	   10000	    116483 ns/op	       0 B/op	       0 allocs/op
PASS
ok  	github.com/pingcap/tidb/expression	3.352s

• Manual test (add detailed scripts or steps below)

mysql> select cast('1234.567' as real);
+--------------------------+
| cast('1234.567' as real) |
+--------------------------+
|                 1234.567 |
+--------------------------+
1 row in set (0.00 sec)

mysql> select cast(x'0102' as real);
+-----------------------+
| cast(x'0102' as real) |
+-----------------------+
|                   258 |
+-----------------------+
1 row in set (0.00 sec)

mysql> 

[sre-bot]

Thanks for your contribution. If your PR get merged, you will be rewarded 50 points.

[XuHuaiyu]

LGTM

[codecov]

Codecov Report

Merging #13445 into master will not change coverage.
The diff coverage is n/a.

@@             Coverage Diff             @@
##             master     #13445   +/-   ##
===========================================
  Coverage   80.3183%   80.3183%           
===========================================
  Files           472        472           
  Lines        114894     114894           
===========================================
  Hits          92281      92281           
  Misses        15407      15407           
  Partials       7206       7206

[pingyu]

/rebuild

[qw4990]

LGTM, WELL DONE!

[sre-bot]

Your auto merge job has been accepted, waiting for 13402

[sre-bot]

/run-all-tests

[sre-bot]

@pingyu merge failed.

[sre-bot]

@pingyu complete task #12105 and get 50 score, currerent score 150.